1. Field of the Invention
The present invention relates to an optimum control method for internal combustion engines which is capable of controlling an engine such that the engine is operated at a minimum rate of fuel consumption.
2. Description of the Prior Art
One of the engine control methods, which have heretofore been proposed for the purpose of reducing fuel consumption, is to preset an ignition timing advance pattern with respect to, for example, engine speeds and intake vacuum as control parameters and the advance pattern is mechanically realized faithfully. Alternatively, engine control variables such as ignition timing, air-fuel ratio and EGR rate (rate of exhaust gas recirculation) are preliminarily arranged in maps with respect to such parameters as engine speeds and intake vacuum which are indicative of the engine operating conditions and the operating conditions of the engine are controlled in accordance with the mapped engine control variables. However, these known control methods are disadvantageous in that these methods can not compensate for the variation in the characteristics of engines over time or the variation in the characteristics of engines caused during manufacture, thus failing to accurately control the rate of fuel consumption.